1. Field of the Invention
The present invention relates to devices for viewing two dimensional photographs or images (such as TV or movies) which then appear to the viewer as three-dimensional. The device is light in weight and has three basic adjustments for establishing the stereoscopic effect. These adjustments are for area of view along the optic axis, for interpupillary distance between the eyes of the viewer, and for the optic axes, themselves. As will be described below, the device is seen to enhance the quality of VCR images generated during playback.
2. Description of the Prior Art
Hand held devices to achieve an apparent three-dimensional display from ordinary two dimensional visual data such as photographs or television displays are known in the prior art. Many of these devices operate in accordance with the teachings of the Ames U.S. Pat. No. 2,542,789. That patent discloses that definite and true depth discrimination may be induced by the differentiating dispostion of some characteristic form elements in the respective dioptric images, irrespective of their position on the retina. U.S. Pat. Nos. 607,172; 1,636,450; 2,297,322; and 2,337,139 show the implementations of the Ames description by tilting one image relative to another with mirrors or refractive elements. U.S. Pat. No. 2,986,969 uses both refracting and polarizing elements to achieve the Ames criterion.
U.S. Pat. Nos. 3,460,882 and 4,049,339 show other techniques for creating the effect of 3-D using illocal framing and "window effect", respectively.
The major difference between the present invention and the approaches and devices of the prior art is that the present invention accomplishes surprising and unexpected results without the use of mirrors, lenses, or other optics. In fact, the results of the present invention are achieved without any other moving parts or optical elements.
The net three-dimensional effect in the present invention is the sum of four distinct and separate processes and their respective effects; but only three of the processes are independent. The first of the four processes is the observation that a strong perception of depth can be observed with only one eye (while the other eye is closed) when a two dimensional display is viewed through a tiny aperture of 1 mm or less in diameter (a "pinhole"). The second three-dimensional enhancing effect occurs when the monocular image of the first process (with its increased perception of depth) is viewed with both eyes, binocularly, by the use of a second aperture. The second effect adds to and enhances the first effect. The third process is that of illocal framing which is implemented by employing frames suspended between the display and the observer. However, the use of the illocal framing concepts implemented in the present invention depends solely on the increased depth of field afforded by the use of the pinholes described above.
As discussed in the aforementioned U.S. Pat. No. 3,460,882 by Abrahamson, "illocal framing" is visible framing that is situated in a plane substantially removed from that of the observed picture itself and near the observer. "Illocal framing" is in contrast to standard framing which is local to the picture it enclosed, or is in direct contact with it. The illocal frame appears situated somewhere between the picture and the observer and has the capability of improving the depth effects. The objects in the picture appear to be more life-size.
The three-dimensional viewing glasses implements illocal framing by positioning the frames by adjusting H, the distance from the pinhole to the frames, within the increased depth of focus range determined by the pinhole diameter. The depth of focus depends on the pinhole diameter but also on the distance of the fixation point from the eye, Physiology of the Eye, Hugh Davson, Academic Press, N.Y., 1980, Page 486. The display is located at the fixation point. With H either within the depth of focus range or close to it, the frames will be, respectively, in focus or almost in focus along with the display under observation. The requirement of illocal framing, to suspend a frame between the observer and the display, is thus met by the use of a pinhole to extend the depth of focus range and allow the frames to come into the same depth of focus range occupied by the display.
An important visual property of the three-dimensional viewing glasses in the "movie theatre effect". A pair of correctly focuses glasses will give the wearer the distint "viewpoint" that he or she is actually inside a movie theatre where the frames now appear as a full size movie screen appearing to be approximately 100 feet away and the theatre's "ceiling" and "walls" (actually, the inside of the input aperture housings) are in their proper perspective and depth relationships as they would be in a real movie theatre.
This effect is caused by three factors. The increased depth of focus afforded by the pinhole, the illocal framing effect of the picture appearing to be more than life size and the visual isolation from the environment afforded by the ambient light shield. The movie theatre effect is especially important when viewing television displays if optimum results are despred.
The fourth process under consideration, is, I believe, a new way of applying and implementing the principles of the Ames U.S. Pat. No. 1,636,450. That patent recognized that an illusory depth or rotundity is caused by the modification of the direction of the viewing axis of one or both eyes. Typically, this is done with the use of refraction and reflection elements as previously discussed. In my invention, modification of the viewing axis is accomplished by spatially positioning a pinhole which defines the optical axis and thus the location of images on the retina. As the pinhole has a three-dimensional effect all of its own, an important part of my invention is the alteration of the viewing axes of the eyes by positioning the pinholes.
Even without pinholes, any obstruction, such as a finger or a half inch wide by two inch long strip of opaque tape, which is placed in close proximity to the eye and is edged slowly into the eyes' field of view will also change the direction of the viewing axis. This effect is not readily observed when done to one eye alone due to the tendancy of the eye to compensate for the restriction in its field by adducting. This is discussed in Physiology of the Eye, H. Davson, Academic Press 1980, p. 520. When done symmetrically and slowly to both eyes simultaneously, a surprisingly excellent three-dimensional representation of two dimensional material will be displayed. By symmetric, it is meant that one obstruction is moved simultaneously into the field of view of the right eye from the left side of the right eye while in the left eye, an obstruction is moved into its field of view from the right side of the left eye. Once stereopsis is detected, the position of the obstruction is maintained. Excessive vignetting is apparent at first but can be minimized with practice.
Stereopsis generated in this manner is caused by a temporal disparity. If however, the obstructions in the above example were symmetrically moved from the temple side (i.e., both left and right temples simultaneously) towards the nasal side, a condition of nasal disparity would be created resulting in "locally inverted" or "locally pseudoscopic like" images. These same effects are also apparent when pinholes are used. The main difference between the two stereo producing techniques is the magnitude of the image vignetting. Vignetting is unavoidable in the case of the obstruction technique and non-existant when using the present invention properly focused.
For a given distance between the device (i.e., its pinhole) and the two-dimensional display under observation, the interpupillary distance, d.sub.i, is adjusted for maximum light throughput, d.sub.mlt. Under these conditions, the observed stereopsis is due soleley to the above mentioned effects and not on the teachings of the Ames patent. When d.sub.i is equal to d.sub.mlt, it is assumed that the axial directions of the eyes are equal to the axial directions that would occur if the two-dimensional display were viewed normally without the three-dimensional viewing glasses of the invention. However, by increasing the interpupillary distance beyond d.sub.mlt, a modification in the direction of the viewing axes of one or both eyes will occur. Under these conditions, the Ames teachings will now apply and the observed stereopsis will increase dramatically with increasing d.sub.i until a condition analogous to hyperstereopsis is reached. Though not necessary, the frames should be readjusted for each setting of the interpupillary distance, d.sub.i. Adjusting the frames enables the principles of illocal framing. Counteracting the increasing stereopsis as d.sub.i is increased are increased image vignetting and a reduction in light throughput for larger values of d.sub.i greater that d.sub.mlt.
In actual use, knowledge or determination of d.sub.mlt is not required for the correct use or adjustment of my invention. however, d.sub.mlt may be determined by looking through the device with its pinholes wide open. While fixating on the display of interest, d.sub.i is adjusted to that size which gives a normal flat display. With the device so adjusted, the point of fixation is said to lie on the horopter and for a given fixation distance will simulate corresponding retinocortical elements.
The selected value of d.sub.mlt may be verified by closing the pinhole down to about 1 mm and adjusting d.sub.i for the minimum three-dimensional effect without image "inversion", This process is hindered by the presence of monocular depth perception introduced by the small 1 mm diameter pinhole. Values of d.sub.mlt selected by the latter method are often within .+-.0.6 mm of the first method.
On the preferred embodiment of my invention, the maximum diameter when wide open was 4.7 mm. This diameter was small enough to be present in the observer's peripheral field of view and cause stereopsis with vignetting as was noted above to occur when an obstruction is symmetrically introduced into the peripheral field of view. Centering the irises within the wide open pinholes will eliminate this extraneous stereopsis, if present.
For d.sub.i less then d.sub.mlt contiguous portions of the observed image will appear "inverted" or "locally pseudoscopic" wherein image elements appearing in the foreground when d.sub.i is greater that d.sub.mlt will now appear in the background and vice versa. This effects is not observed in television displays due to their relatively low spatial resolution. This local pseudoscopic effect can be shown to exist even when the photographic display under consideration consists only of contiguous color differences with no perspective information.
Of the three independent processes under discussion, the pinhole process plays the key role. This is because the pinhole process is in effect at all times, while the other two processes, Ames and illocal framing, are not. In addition, the pinhole process allows the "seamless" integration of all three independent processes without the use of optical elements.
The small pinhole aperture selected achieves a number of beneficial results in the invention. The pinhole increases the observer's depth of focus thereby reducing the accommodating capability of the single eye. Elimination of accommodation results in improved monocular depth sensation.
The pinhole aperture increases the sharpness of any given display in addition to reducing noise in television images because of five interrelated factors which include:
1. The fact that light passing through a pinhole is, in a sense, automatically focused where the focal length of the pinhole is defined as the square of the diameter of the pinhole divided by the wavelength of the transmitted light. See M. Young, PInhole Optics, Applied Optics, Vol. 10, No. 12. Dec. 1971, p. 2764;
2. The increase in depth of focus due to the reduction in pupil size;
3. The spatial smoothing (i.e. low pass optical spatial filtering) of the television image caused by restricting the optical spatial frequencies entering the eye by decreasing the diameter of the exit pupil (i.e., the pinhole). This cut off eliminates those spatial frequencies responsible for high resolution image detail (i.e., video noise). With these high frequency components removed, their associated noise will be filtered components removed, their associated noise will be filtered from the image recorded on the retina;
4. The measured increase in the response of the Modulation Transfer Function of the refractive optics of the human eye as the pinhole is closed down from its wide open position (of about 5 mm) to a limiting diameter of 3 mm. Ian Overington, Vision and Acquisition, Pentech Press, London/Crane, Russak & Co. Inc., N.Y., 1976, p. 12;
5. A reduction in the veiling glare entering the eye.
The three-dimensional viewing glasses improves the overall appearance of a color television display and is especially effective during the playback of recorded VCR (video cassette recorder) images. Observing a television display through the device results in a visual smoothing (i.e., a spatial averaging) of the image where television raster lines and finely structured time dependant white speckled noise are substantially reduced. The reduction of this noise results in an apparent improvement in the resolution of the video display in spite of an objectively measured loss in resolution. It has been mentioned (Overington, p. 188) that with noisy pictorial displays and television pictures, blurring results in an increase in the detail information visualized in the display. Television is particularly sensitive to this effect.
An actual loss in resolution can be objectively measured by illuminating a standard resolution target and observing it from a distance of 1.6 meters. In this test, lines separated at 1 mm could be easily resolved without the pinholes but could not be resolved with the 0.8 mm diameter pinholes in place.
When located in as close proximity to the cornea as possible, the pinhole will largely negate the use of the viewer's cornea and lens. However, some residual focusing (or accommodation) is still possible by the eye's lens (Hennessy, R.T., Iida, T., Shina, K., Leibowitz, H.W., "The Effect of Pupil Size on addommodation", Vision Res., Vol. 16, pp. 587-589, 1976).
Pinhole images are inverted and at a fixed distance from the pinhole to the retina, focusing is accomplished by closing the pinhole to improve the depth of field. Because of the five factors under discussion, persons wearing mild prescription eyeglasses who remove them to use the three-dimensional viewing glasses of the invention may experience a significant improvement in normal visual resolution over that received had they worn no eyeglasses. In most instances, these viewers will experience and improvement in normal visual resolution equal to that received with their own prescription eyeglasses. For one observer with +0.5 diopter corrective lenses, this optimum resolution occurred at a pinhole diameter of 1.1 to 1.2 mm at a 1.6 meter viewing distance. The object viewed was a standard test target. Smaller pinhole diameters worsened the resolution at this 1.6 meter viewing distance. However, this was not true for a television image viewed at this same distance. In this instance, the apparent resolution of the video image continues to improve as the pinhole is reduced. Optimum video resolution was obtained with a pinhole diameter of 0.8 to 0.9 mm.
Finally, the pinholes allowed the placing of an optically focused frame in front of the display in connection with the illocal framing techniques discussed above in U.S. Pat. No. 3,460,882.
For any given display, the quality of the perceived three-dimensional effect will depend on the specific requirements of the display including the display's brightness, resolution, viewing distance and image content.
In general, sharp lithographic or photographic material produces the most dramatic three-dimensional results. Television produces good results, while normal movie screen illumination levels are not sufficient for adequate operation of the three-dimensional viewing glasses. This may be corrected in principle by making provisions to increase the screen illumination levels.
Illocal framing is a necessity when viewing television displays. It can be dispensed with, however, when observing photographic of printed (lithographic) material.
When observing a 19 inch diagonal screen color television close up at viewing distances of approximately 36 inches, a small pinhole (0.70 mm) is desirable. If this same image is viewed at a distance of say 63 inches, a pinhole setting of 0.90 mm is found to be more suitable. More importantly, at either viewing distance, varying d.sub.i has virtually no effect on the resulting television image; the Ames process results in no discernable stereopsis at normal TV resolution specifications.
Typically, a small pinhole is required when observing photographic or printed material close up (15-34 inches). However, the size of this pinhole can vary between 1.10 and 0.75 mm depending on the available illumination, the resolution in the image, and the specific viewing distance.
Suitable illumination levels for pictorial material can be established by illuminating the material with a 100 to 150 Watt household light bulb positioned to eliminate specular glare at a distance of about 12 inches from the display material.
The best pinhole diameter for a standard resolution (0.20 mm dot separation) lithographic print observed at a viewing distance of 63 inches was found to be around 1.5 mm. Different results should attend different observers.
The invention can be used as a sports or scenic viewing glass since the need to refocus the eye for distant or near objects being observed is eliminated. A field of view of 30 degrees attends this mode of operation. This mode substantially reducers viewer fatigue. It is noted that the invention's increased depth of field allows ordinary objects to be examined, without fatigue, at distances closer than the normal viewing distance of 25 cm.
The principle object of the present invention is the provision of a device which results in a three-dimensional viewing system posessing a degree of stereopsis judged comparable to normal stereoscopic photography which uses two dissimilar images of the same object.
Another object of the present invention is the construction of a device of the simplest possible design employing no transmissive or reflective optical elements which add to costs, complexity, and to interference since such elements are sources of noise and are difficult to use.
A further object of the present invention is to produce a device of the class described which has extreme optical clarity.
Another object of the present invention is to provide the viewer with increased spatial resolution when the invention is used to view television.
A further object of the invention is to provide a two dimensional object with a three-dimensional perspective without the need for the viewer to wear their normal eyeglasses.
Another object of the invention is the provision of an optical device which substantially reduces playback noise in recorded VCR images resulting in an increase in the observed signal-to-noise ratio in these images when same are viewed through the invention.
A further object of the invention is the provision of a stereoscopic viewer which can be used to examine objects which are both nearby and distant without the fatigue caused by continual changes in focusing.
An additional object of the invention is the provision of a 3-D viewer which can be used to examine objects located extremely close to the viewer without the need to refocus and without the resultant fatigue.
Another object of the present invention is the provision of a two dimensional to three dimensional viewer which is light in weight to allow for comfortable mounting on the viewer's head over the eyes in the manner of goggles.
A further object of the invention is the provision of a device which provides apparent three-dimensional visual displays using ordinary two dimensional visual information such as photographs and television displays.
Another object of the invention is the generation of three-dimensional effects from two dimensional displays without the necessity for any special prerecorded visual or other information to create the 3-D effects.